1. Field of the Invention
The present invention relates to a thermal analysis apparatus capable of measuring a thermophysical property of a sample, which changes along with a temperature change, and of imaging and displaying the sample.
2. Description of the Related Art
Among the thermal analysis apparatus, a differential scanning calorimeter is a thermal analysis apparatus in which temperatures of a sample and a reference substance received within a furnace are changed based on a constant rate program, and a temperature difference between the sample and the reference substance is detected, thereby measuring the temperature difference to obtain a heat flow difference. There is known an apparatus which is obtained by combining the differential scanning calorimeter as described above with means for imaging the sample within the furnace, and which records an image of a change in sample state as image data along with a change in heat quantity of a sample under measurement, to thereby enable a change in sample substance to be analyzed in more detail (Japanese Patent Application Laid-open No. Hei 08-327573).
In Japanese Patent Application Laid-open No. Hei 08-327573, one layer of a transparent observation window made of quartz glass is newly provided to a lid portion in the upper part of the furnace generally constructed of a non-transparent metal material or the like, and further, imaging means for imaging a sample within the furnace is combined therewith, to thereby record a sample state at the time when temperature rises and drops as image data along with a DSC curve. This enables a change in sample state to be grasped correctly, which is difficult to determine based only on the DSC curve.
Further, there is provided a differential scanning calorimeter including the same imaging means, which has transparent observation windows provided not only to the lid of the furnace but also to the upper part of a furnace cover that covers the periphery of the furnace, and in which purge gas is supplied to the transparent observation windows to suppress dewing and frosting occurring on the observation windows in a low temperature range (Japanese Patent Application Laid-open No. 2001-183319).
Further, there is disclosed a differential thermal analysis apparatus including a sample cylinder for receiving a reference substance and a sample, and a side wall of an outer cylinder thereof, which are made of a transparent material, to thereby visually recognize the state within the sample cylinder (Japanese Patent Application Laid-open No. 2001-33410).
It is preferred that the lid portion of the furnace of the thermal analysis apparatus have high thermal conductivity and an even temperature state, originally. However, in the thermal analysis apparatus described in Japanese Patent Application Laid-open No. Hei 08-327573, the transparent observation window, which is used for observing a sample and is provided to the lid in the upper part of the furnace, is made of quartz glass, and hence the thermal conductivity is poor and uneven temperature distribution is likely to be generated in the window portion due to an influence of disturbance of the environment outside the furnace. Further, the transparent observation window is formed of one layer, and hence the above-mentioned uneven temperature distribution generated in the observation window may easily be spread to the inside of the furnace, with the result that the influence of the disturbance may easily be imposed on temperature distribution within the furnace and temperature distribution of gas within the furnace. Meanwhile, a differential heat flow detection portion installed in the furnace has high sensitivity so as to detect a minute temperature difference between the sample and the reference substance. Therefore, the differential heat flow detection portion may detect, as a signal, the influence of the disturbance imposed on the temperature of the furnace lid, the temperature within the furnace, or the temperature of the gas within the furnace with high sensitively via solid thermal conduction and gas thermal conduction, or radiation. As a result, the uneven temperature distribution generated by the disturbance of the environmental temperature in the transparent observation window formed of one layer may cause distortion, fluctuation, and the like in the DSC curve. This leads to a problem that it is difficult to obtain a stable and accurate DSC curve.
As to the technology described in Japanese Patent Application Laid-open No. 2001-183319, transparent observation windows are provided not only to the furnace lid but also to the upper part of the furnace cover that covers the furnace, which means that two layers of transparent windows are provided. However, though the furnace is required to ensure a stable temperature distribution under precise temperature control for a thermal analysis/measurement, the observation window of the furnace lid provided to the upper part of the furnace portion is formed of one layer, which leads to the same problem as in Japanese Patent Application Laid-open No. Hei 08-327573.
Also in Japanese Patent Application Laid-open No. 2001-33410, the transparent material portion formed in the side wall of the sample cylinder is formed of one layer, which leads to the same problem.